MEETING OF THE MINDS: Jonathon Niese (right) talks with catcher Ronny Paulino on the mound during the Mets' 6-2 loss to the Cardinals yesterday at Citi Field. Paul J. Bereswill

Already, Jonathon Niese had made one big mistake, leaving a pitch up in the first inning that Albert Pujols deposited in left, about a mile and a half from home plate. So with Cardinals’ starter Jake Westbrook zipping through the Mets with a heavy sinker, Niese faced a 2-1 deficit and had little margin for error.

Then came the error-filled fifth. Yes, the Mets in the field ripped a page from their 1962 history, plunking a runner with a throw on a possible double-play grounder and later throwing from the outfield to an uncovered base. But Niese himself committed the worst blunder of the inning. He walked the pitcher, Westbrook, setting up a first and second, one-out scenario. Then all Hades broke loose as the Mets put their defense on display.

“I just didn’t execute my pitches. It was one of those things where I wasn’t trying to walk him. But those pitches got away from me and the last pitch cut on me. I didn’t want to, but it happened,” Niese (9-8) said of the walk, which fueled the bizarre, three-run inning in the Mets’ 6-2 loss to the Cardinals. “It really didn’t help matters out obviously. Getting that out would have been big, but that’s not how it played out.”

Still, Niese did not pitch poorly overall. The lefty threw six innings, allowed three earned runs, five hits and struck out seven — which gave him a total of 33 strikeouts in 31 2/3 innings over his last five starts (9.38 per nine innings since June 25). Niese lost for only the third time in his last 11 decisions.

“I thought he pitched very good. He had good command. He was strike one on a lot of guys and his sinker was working very well,” said manager Terry Collins, who lifted the starter for a pinch hitter in the sixth. “To me, he made one mistake: he threw a sinker to Albert and he got it up and [Pujols] did what he does best. If we play defense in the fifth, it’s a 2-1 game.”

All of that is little comfort to Niese. Pitching well and winning are different matters. Especially with Westbrook getting 17 of 24 outs in a season high-tying eighth innings through ground balls.

“I felt like my stuff was good enough,” said Niese, who lamented the ninth pitch of Pujols’ first-inning at bat that became the Cardinal stud’s 21st homer. “I left that pitch up to Pujols. He put a good swing on it. Just one of those days. You feel good and things don’t go your way.”